1. Field of the Invention
The present invention relates to a pneumatic tire provided, on a tread surface, with a circumferential groove which extends in a tire circumferential direction, a land portion which is zoned by the circumferential groove, and a plurality of lug grooves in which one end is open to a side of the circumferential groove and another end is terminated within the land portion.
2. Description of the Related Art
As a tread pattern of the pneumatic tire, there has been frequently employed a tread pattern provided with a circumferential groove which extends in a tire circumferential direction, a land portion which is zoned by the circumferential groove, and a plurality of lug grooves in which one end is open to a side of the circumferential groove and another end is terminated within the land portion, and structured such that the land portion has a rib-like portion which is successive in the tire circumferential direction and a wing portion which is zoned by the lug grooves.
In Japanese Unexamined Patent Publication No. 2007-90944, there is disclosed a pneumatic tire in which the land portion has the rib-like portion and the wing portion as mentioned above, characterized in that a lot of small holes are provided in a tire ground surface side of the wing portion.
However, in the pneumatic tire of Japanese Unexamined Patent Publication No. 2007-90944, it has been known that a rigidity of the wing portion is lowered by provision of the small holes in the tire ground surface side of the wing portion, and a steering stability is deteriorated due to a weakness in a lateral force. Further, if the rigidity of the wing portion is lowered, a rigidity difference between the rib-like portion and the wing portion becomes larger, and it has been known that such irregular wear that the rib-like portion preferentially wears in comparison with the wing portion comes into question. Further, since the wing portion tends to be deformed back and forth in comparison with the rib-like portion at a time when the force in the tire circumferential direction is applied to the land portion, a bending moment is generated on a trailing end portion of the lug groove as a base point, and a strain becomes maximum at the trailing end portion of the lug groove. It has been known that the strain causes the irregular wear.